CUBIZEN: Global Mapper, CityEngine & Creative Tech

What Is Viewshed Analysis in Global Mapper?

Following our previous session, today we will dive intoViewshed Analysisin Global Mapper.

Viewshed Analysis is commonly used to evaluate how a project or development affects visible areas within a landscape. It is an analytical process where you select key viewpoints and look toward the project site to compare the current status with the planned state to see how much the visibility changes. (In many real-world projects, analysts evaluate only the existing visibility conditions.)

In the past, when performing viewshed analysis including buildings in software like Q-GIS or Arc-View, you had to convert the buildings into a DEM (Digital Elevation Model) and overlay them on the terrain. However, Global Mapper offers a major advantage: it allows you to analyze building vector data directly without converting it to a DEM. This capability has been available in Global Mapper for more than a decade, and while other programs might support it now, it has long been a standout function here.

Let's get started.

Since modifying building attribute values is a separate task, today we will focus solely on the terrain for this demonstration.

How to Perform Viewshed Analysis in Global Mapper

Step 1: Load Your Workspace

First, load the Workspace we created in the last session.

If you have loaded the work from the previous session, your screen should look something like the state shown below.

Step 2: Accessing the Viewshed Tool

From the icon toolbar, select the Create Viewshed icon (it looks like a lighthouse beam or a signal coming from a mountain top).

Upon clicking, a tip message will appear with some instructions and a prompt to pick the starting point for the analysis.

Check "Don't Show This Again" and click OK.

Step 3: Selecting the Observation Point

Your mouse cursor should have changed. Click on the map to define the observer location for the analysis.

Step 4: Viewshed Setup and Parameters

Once you click, the Viewshed Setup window will appear. Here is a breakdown of the key settings:

Understanding Viewshed Parameters

To get the most accurate and meaningful simulation results, it is essential to understand how each parameter behaves in a real-world workflow:

• Layer Name: You can enter a custom name for the new layer that will be generated. Organizing these layers by description or date is highly recommended when running multiple scenarios.
• Transmitter Elevation: This represents the observer's viewing height above the terrain surface. By default, it is set to 1.6 meters, which perfectly mimics the average human eye level. If you are simulating a security camera or a viewing deck, remember to adjust this value to the actual structure height.
• View Angle & Start Angle: This sets the starting azimuth and the horizontal range of the analysis around the observer. The Start Angle defines where the arc begins clockwise from North (0 degrees), while the Swept Angle determines the total span of the arc. For instance, a Start Angle of 290 and a Swept Angle of 60 means the analysis covers from 290 degrees to 350 degrees. This is incredibly useful for restricting the analysis to a specific field of view, such as a window or a camera lens.
• Earth Curvature: Check this option if you want to include or ignore the earth's curvature. While it doesn't impact short-range, localized projects, enabling curvature correction is absolutely critical for long-range environmental assessments or coastal visibility studies.
• Display Color: Choose a highly contrasting color for the visible areas to ensure it stands out clearly against your underlying terrain or aerial imagery.
• View Radius: Defines the maximum distance from the observer that the analysis will reach. Setting this too wide can increase processing time unnecessarily, so it is best to match it with the actual scope of your visual impact assessment.
• Sample Spacing: Sets the resolution or cell size for the analysis grid. Smaller values provide much higher accuracy for detailed urban modeling but require more processing time, whereas larger values are ideal for quick, large-scale preliminary drafts.
• Use Vector Features with Heights: Enabling this allows vector elements (like 3D building footprints) with height attributes to be included directly as obstructions. This is Global Mapper's strongest advantage, allowing you to bypass tedious DEM conversion processes entirely.

Once you have carefully configured these settings based on your project requirements, click OK to run the simulation.

Step 5: Reviewing and Refining the Results

The calculation will run quickly, and the final results will be displayed instantly as a new vector overlay on your map!

The shaded areas represent everywhere that has a direct, unobstructed line-of-sight from your chosen viewpoint. If certain zones are unexpectedly hidden, it is usually due to micro-topography or nearby structural obstructions defined by your vector data.

If you wish to modify an existing viewshed analysis to test a different scenario, you don't need to start over. Simply right-click the corresponding layer in the Control Center and select "Edit Viewshed Parameters and Recalculate." This opens the setup dialog box again, allowing you to adjust parameters—such as increasing the observer height or expanding the radius—and refresh the analysis instantly.

Advanced Viewshed Analysis Features

Since this is a brief overview, I've kept it simple. While we used a mouse click to set a point today, you can also:

• Register specific viewpoints as a layer and analyze them.
• Select dozens of points at once for batch processing.
• Overlap visible areas to determine "Visibility Frequency."
• Import building data, assign height attributes, and include them in the simulation.

WWhile it is not intended to replace dedicated high-end 3D simulation platforms, for general GIS workflows, Global Mapper is incredibly convenient for "setting the stage" and getting reliable results quickly.

I assume those who find their way here searching for Global Mapper already handle at least one GIS tool for their professional work. I'm presenting this as a high-level overview so you can compare it with the tools you currently use.

That’s all for today!